Studies have been made to build and standardize IMS (IP Multimedia subsystem) networks by 3GPP (3rd Generation Partnership Project) for the purpose of flexibly providing voice, video and other multimedia applications on packet communication networks based on IP (Internet Protocol) technologies, and various technologies related thereto are described in Patent Documents 1 to 3, and Non-Patent Document 1, for example.
FIG. 9 is a conceptual diagram showing IMS network configuration. A SIP (Session Initiation Protocol) terminal (1) is a subscriber terminal in the IMS network. A P-CSCF (2) is a SIP server with a proxy call session control function for direct access from the SIP terminal (1). A S-CSCF (3) is a SIP server called S-CSCF (Serving CSCF) which is located within a service provision area of a provider to which the SIP terminal (1) directly subscribes. An AS (4) is an application server which controls a common enabler connected to the S-CSCF (3) to be shared by various services or controls each of the services. An HSS (5) is a home subscriber server storing user subscription information.
The location of the SIP terminal (1) is registered by performing registration procedures (user registration procedures) through a Gm-I/F using a SIP protocol, whereby the SIP terminal (1) is enabled to enjoy IMS services including transmission/reception services through the IMS network, using VoIP (Voice over Internet Protocol).
Upon receiving a SIP REGISTER signal from the SIP terminal (1), the P-CSCF (2) acquires information on the S-CSCF (3) providing the IMS service, from the HSS (5) serving as the subscriber database through Dx-I/F using Diameter protocol, and transmits the SIP REGISTER signal to the S-CSCF (3) through Mw-I/F using the SIP protocol. Further, upon completion of the registration procedures, the P-CSCF (2) holds registration information such as the IP address of the SIP terminal (1) and the IP address of the S-CSCF (3) to perform relay control of SIP signals in the subsequent IMS services
Upon receiving the SIP REGISTER signal from the P-CSCF (2), the S-CSCF (3) acquires subscriber data from the HSS (5) through Cx-I/F using Diameter protocol and holds the same, so that the subsequent transmission/reception services are performed according to the subscriber data. Further, the S-CSCF (3) transmits the SIP REGISTER signal to the AS (4) through ISC-I/F using the SIP protocol, according to iFC (initial Filter Criteria) information contained in the subscriber data from the HSS (5). Upon completion of the registration procedures, the S-CSCF (3) holds registration information such as the IP address of the P-CSCF (2) to thereby enable routing to the P-CSCF (2) during a reception service.
Upon receiving the SIP REGISTER signal from the S-CSCF (3), the AS (4) acquires subscriber data from the HSS (5) through Sh-I/F using Diameter protocol and holds the same, so that the subsequent transmission/reception services are performed according to the subscriber data. The HSS (5) is a subscriber database for managing service data of all the subscribers, and transmits the subscriber data in response to a request from the S-CSCF (3) or the AS (4). Further, the HSS (5) notifies the P-CSCF (2) of the S-CSCF (3) performing the registration control in the registration procedures, and holds the address of the S-CSCF (3) of which the notification was made.
As described above, the IMS network downloads, from the subscriber database HSS (5), subscriber data required by the S-CSCF (3) or AS (4) to perform transmission/reception service according to the SIP REGISTER signal from the SIP terminal (1), and provides a service according to the subscriber data upon receiving a request for services including transmission and reception from the SIP terminal (1).    Patent Document 1: Japanese Kokai Patent Publication No. 2005-064646    Patent Document 2: Japanese Kokai Patent Publication No. 2006-109478    Patent Document 3: Japanese Kohyo Patent Publication No. 2006-517064    Non-Patent Document 1: “Series: IMS Becoming Core of NGN”, WBB Forum